Selecting A Seal
It must first be decided whether the sealing element is to be synthetic rubber or leather. Many factors determine this, for example, media to be sealed, temperature, shaft speeds, surface finish, etc., and all must be carefully considered.Generally leather elements would be more used for more arduous applications having moderate shaft speeds, pressures and temperatures of -30°C ti +90°C (-13°F to +194°F). Synthetic rubber (nitrile®) seals will accommodate temperatures of -25°C to +120°C (-13°F to +248°F) and, by the very nature of their design, greater surface speeds and pressures.
With sophisticated rubber we are able to increase the temperature range quite considerably, for example, silicone rubber -60°C to +200°C (-76°F to +392°F) and fluoroelastomer (FPM) rubber -15°C to +250°C (+5°F to +482°F). It must be stressed however, that these are the maximum limits for the material used and must be grouped together with the other application details before final selection is made. EPM would be pleased to offer advice on the correct materials, should the need arise.
Also available are the following variations of seal design, which are not illustrated on this site but identified by suffix letters:
Seals should be stored at room temperature in a clean, dry atmosphere. They should be kept in the protective paper in which they are received until they are ready for assembly.
If the nature moisture found in leather dries out during storage and the element becomes hard, you will restore flexibility by soaking them in warm oil at 25/30°C (77/86°F) for not less than 15 minutes. Before commencing this operation, however, the source of heat must be removed. Do not throw seals into bins, stack them in irregular piles or tie them up with string or wire. Treat them for what they are – an important engineering component.
FITTING A SEAL
Having satisfied yourself in this respect, apply a thin film of general purpose grease to the sealing element to assist assembly. This is imperative in case of synthetic rubber. Dual/Triple seals need to have the cavity between the lips pre-packed with grease, as there is a danger that one of the lips may not receive adequate lubrication under working conditions. By applying this grease the life of this type seal will be greatly increased.
Care must always be exercised when assembling seals on to the shaft to avoid damage to the sealing edge. If a lead-in chamfer/radius has not been provided or if the seal has to pass over a key-way, then it is necessary to provide a fitting sleeve as illustrated. Noncompliance with these instructions can lead to either the lips being turned back or cut, particularly in the case of rubber. There is also the possibility of the spring becoming dislodged, which, after the element has been returned to its normal position, will mean there is a danger of it making contact with the shaft, with the resultant disastrous effects. The application of a liberal smear of grease on the internal side of the element will greatly assist the seals assembly.
DIRECTIONS OF SEALS
This is particularly advantageous in grease lubricated applications as this will allow the discharge of any contaminated lubricant from the sealing area when the grease gun is applied. This will then ensure clean lubrication of the seal lip and reduce unnecessary wear from abrasive elements.
If there is no alternative but to use the old seal then do take extra care: